The rigid catenary is a power system for rail transport alternative to the conventional catenary and which basically consists of an aluminium profile with an area in the form of a gripping device which serves as housing to the copper contact wire whereby it makes contact with the pantograph table positioned in the locomotor roof, thereby capturing the line current.
Despite the fact that its lower maintenance costs compared with conventional catenaries justify its installation in any part of the line, its use is normally almost exclusively restricted to the inside of tunnels since it reduces the gauge necessary therein. The fact that this electrification system is not widely used justifies that most of the section insulators are designed to be adapted to conventional catenaries and not rigid catenaries.
The overhead contact lines installed to supply electricity to the railway lines are subdivided in different sections or electric circuits to thus guarantee its operating availability. This sectioned design of the electrical installation enables the insulation of each of the sections independently, so that the power supply can be interrupted without having to cut the current supply to the entire installation. In this way, in the event that a fault occurs in one or several sections comprising the line (either the service is interrupted in a planned manner to perform periodic maintenance work or repair in the event of fault) the power supply is guaranteed, and therefore the operation of those sections that are not affected by said circumstances, thus avoiding the interruption of the rail traffic throughout the line.
To achieve this purpose, the aforementioned section insulators are used, which consist of insulating elements which, positioned between two adjacent sections of overhead contact line, interrupt the electrical continuity between said sections although they guarantee the mechanical continuity between both, thus allowing the passage of the pantographs. The section insulators should maintain the electric voltage in the pantograph, guaranteeing that the protection devices of the rolling stock are not affected nor are operating malfunctions created therein, thus avoiding the unnecessary triggering of the protection apparatus. Therefore, the configuration of said section insulators should be such that it permits the pantograph to come into contact with one of the ends of the insulator before losing contact with the other end. The most typical solutions in the state of the art consist of disposing two shoes which guarantee the continuity of the current at the time of passage through the insulator or splitting the contact wire in two, thus establishing a common contact area.
To electrically separate two adjacent sections of the overhead line supplied from two different substations the so-called neutral sections are interposed between said sections. The interposition of these sections enables separating sections between which there is a power difference, in the case of DC, or even a phase difference in the event that the feed current of the catenary is AC. The application is even known of neutral sections of considerable length in transition areas between the supply of DC and AC current, thus making a light rail system compatible with the metro system or even the network of regional trains. In classic designs, the neutral section is defined by the intermediate space, insulated or earthed, which is created between two section insulators or two air gap insulations.
As in the case of the section insulators, the neutral sections, aside from electrically insulating the two sections between which they are installed, must guarantee the mechanical continuity between both so that they enable the smooth passage of the pantograph. Nevertheless, unlike what occurs in the case of conventional section insulators, when the pantograph traverses the neutral section, the electrical derivations between the sections that said neutral section separates must be avoided. For this reason, to reduce the appearance of electric arcs, some systems use track magnets which automatically disconnect the power of the rolling stock when this approximates the neutral section, re-establishing the power immediately after crossing it, for which reason it incorporates a second set of magnets of a function programmed for “time out” in the system which controls the traction of the train or electric traction vehicle concerned.
Despite the fact that, as has been indicated, the rigid catenary is an electrification system which is not widely used and, therefore, most of the existing insulator designs do not adapt to this type of overhead line, there are some appropriate designs for its installation in this type of catenary.
Thus, for example, an insulator assembly can be found in the state of the art applicable to rigid catenaries which is inserted between two conductor rail bars, the ends of said insulator having the same profile as the conductor rail wherein it is inserted. The central part of the insulator is made of a material of great dielectric and mechanical rigidity, so that it complies with the requirements of this type of device: on the one hand, it interrupts the electrical continuity between the two conductor rail bars and further guarantees the mechanical continuity between both, permitting the passage of the pantographs. Shoes are mounted on each side of the insulator, in longitudinal direction, which receive the passage of the pantograph, the central part remaining at an upper level, for which reason the pantograph only rests on the side shoes and not on said central part.
The previous insulator assembly has the advantage that compared with other known insulators it can act as both section insulator and neutral section insulator by doing no more than establishing the appropriate electrical connections in each case. For this purpose, the insulator has copper strips which allow making bridging connections, so that the side shoes remain electrified, thus guaranteeing the power supply to the pantograph during its passage through the insulator. However, when the operating requirements demand the existence of a neutral zone, the bridging cables are removed and in this way, the side shoes are not electrified, so that the pantograph stops being electrically supplied on passing through the central zone which, on being electrically insulated, starts to behave as a neutral area. This functionality, however, obliges introducing a great separation between the side shoes in order to main the necessary safety distances to guarantee the electrical insulation between the different components.
Among this device's deficiencies, and which the insulator object of this invention tries to resolve, we should highlight the difference between the mechanical properties of the rigid catenary and the section insulator, which causes a discontinuity in the vertical rigidity of the system which leads to the appearance of hard points, with the consequent deterioration of the current capturing quality when configured as section insulator.
On the other hand, an undesirable behaviour of this type of section insulator has been observed in combination with pantographs which have a non-uniform wear of the collecting shoes, a phenomenon which is closely linked to the distance between the side shoes already mentioned. On passing through the insulator, the pantograph first rests on the contact wire inserted in the conductor rail profiles positioned at the ends and later in the side shoes of the central zone, which are found at the same height as said wire. On passing through the intermediate zone, wherein the three wires overlap, if the pantograph table is new or has uniform wear, the support is produced correctly and, therefore, the insulator's behaviour is that desired. However, on the occasions wherein the collecting shoe of the pantograph has a high degree of irregular wear, said wear being greater in the central area, there is a high risk of a collision of the sides of the table with the side shoes of the insulator. Sudden bumps against the shoes produce the breaking thereof and, furthermore, as a consequence of the bump, contact losses may occur with the central wire, increasing the wear caused by the appearance of electric arcs.
To avoid these bumps insofar as is possible, it is necessary to adjust the height of the shoes acting on the vertical studs which support them, thus avoiding the collision of the pantograph with the side shoes, even in the case that the pantograph in question has the table worn. Despite the fact that this solution is very simple, it is not of practical use, since logically, the wear of the table of each one of the pantographs which traverse the insulator will considerably vary from one to another, which means it would be necessary to adjust the height of the shoes prior to the passage of each vehicle, which is absolutely infeasible. However, this solution causes a geometric continuity in the height of the different elements of the section insulator, in addition to requiring frequent maintenance operations.
In light of the above, the objective of the present invention is to develop an insulator for rigid catenary which performs the dual function of section insulator, interrupting the electrical continuity between the sections when necessary, and neutral section, guaranteeing in both cases sufficient mechanical continuity between the catenary and the insulator to permit the smooth passage of the pantograph. It is likewise desirable that the insulator in question overcomes the drawbacks of the similar known devices, which means that their configuration should be such that it minimizes the need for adjustment and maintenance and has, insofar as is possible, similar mechanical properties to those of the rigid catenary wherein it is installed.